Justification:
The Megamouth Shark (Megachasma pelagios) is a very large, pelagic filter-feeding shark distributed in pelagic habitats from approximately the surface down to 1,500 m in tropical waters worldwide. The colouration and catch records of the Megamouth Shark are suggestive of epipelagic rather than deepwater habitat, as is the composition of its liver oil. It is known from only 102 specimens (as of August 2015), and therefore appears to be very rarely encountered throughout its range, yet likely to be increasingly taken as bycatch in oceanic and offshore fisheries. Further research on its ecology and habitat use are required to better understand this species and the potential effects of fishing. Based on its wide range, at present it is assessed as Least Concern. Its increasing frequency of capture in Asia, particularly Taiwan, and its rarity and intrinsic sensitivity to overexploitation mean that captures in fisheries should be tracked carefully to ensure this species does not become threatened in the near future.

The Megamouth Shark is currently (August 2015) known from 102 specimens (http://sharkmans-world.eu/mega.html) from tropical and temperate areas of all major oceans. Considerably more specimens are known from the Pacific Ocean in areas such as Taiwan, Japan, the Philippines, and Indonesia than elsewhere. It is probably wide-ranging and circumtropical in its distribution (Ebert et al. 2013).

A coastal and oceanic, pelagic and neritic species, it has been found in water as shallow as 5 m in a bay, 40 m deep on the continental shelf, and offshore in the pelagic zone at 8-1,500 m depth in water 348-4,600 m deep; some specimens have washed ashore (Yano et al. 1997, Ebert et al. 2013). The maximum reported size is 577 cm, although larger unsubstantiated sizes have been reported. The smallest known specimen was 177 cm, but it is unknown if this is close to the size at birth.The only known prey of this species are epipelagic and mesopelagic euphausiid shrimp, copepods and jellyfish (Yano et al. 1997), and it has been suggested that the Megamouth Shark may follow vertical migrations of euphausiid prey during diel cycles (Compagno 2001). The feeding structures of this shark may allow it to feed on other pelagic invertebrates and even small fishes, but so far the stomach contents studied suggest that it primarily targets euphausiid shrimp (Compagno 2001). Observations made on a live-captured Megamouth Shark which was later tagged with an acoustic telemetric tag and tracked for two days, suggested it could breathe readily by gill-pumping and was not dependent on constant swimming like other lamnoid sharks. During the tracking period, the shark revealed a pattern of vertical, crepuscular migration in the epipelagic zone. The mode of reproduction is probably aplacental viviparous with uterine cannabilism or cannibal vivipary suspected in the form of oophagy (Ebert et al. 2013). A late immature or early adolescent female had two ovaries with many tiny oocytes, while an adult female had numerous larger oocytes. This is similar to the ovaries of other lamnoids.

The Megamouth Shark is taken as rare, incidental bycatch of various high-seas and coastal fisheries, including commercial drift gillnets, set fish traps, and pelagic longlines, purse-seines, and pelagic trawls. So far, most specimens have been utilized by museums and oceanaria for research and display. The increasing reports of captures from Southeast Asia suggest some potential effects of fisheries. However, the lack of catch data and life history information makes it difficult to understand the effects of these catches. Dulvy et al. (2014) predicted, based on its body size and depth distribution, that the Megamouth Shark had a high likelihood of being threatened with an elevated risk of extinction if it was subjected to significant fisheries. There is evidence that the Megamouth Shark is frequently captured in Taiwanese gillnet fisheries (D. Ebert, pers. comm., 2015) and there have been recent captures in the Philippines and Sri Lanka (Fernando et al. 2015) raising concern that the level of capture may lead to global population decline.